Radio frequency identification (RFID) devices are used in the form of RFID labels or RFID tags to associate objects with an identification code that may be read or programmed at a distance by stimulating the RFID device with a radio frequency (RF) interrogation or programming signal. Typically, an RFID device consists of an active or passive semiconductor chip assembled with an antenna to receive RF energy from a reader and to transmit or reflect RF energy to the reader in response to an interrogation or programming signal.
High volume manufacturing methods and systems have been developed to produce RFID devices. One system, developed by Alien Technology Corporation of Morgan Hill, Calif., and described in U.S. Pat. No. 6,683,663, utilizes a fluidic self-assembly (FSA) process to deposit RFID chips in a flexible plastic web substrate material having recessed regions to hold the RFID chips. In subsequent operations, a flexible plastic tape material is bonded to the web material to capture the RFID chips, holes are opened over small electrical contact areas on the chips and larger electrical contacts, suitable for attaching an antenna, are screen-printed on the tape material. Each RFID chip with its associated electrical contacts on the flexible substrate assembly is referred to as an interposer, or alternatively as an RFID strap.
FIG. 1A illustrates one example of an RFID strap 100 and FIG. 1B shows a cross-section through RFID strap 100. RFID chip 101 is deposited in recess 102 of web material 103. The RFID chip is laminated between web material 103 and tape 104. Holes 105 are formed through tape 104, and two electrical contacts 106-1 and 106-2 are deposited through holes 105 and on the surface of tape 104. FIG. 2 illustrates an array of RFID straps 200 on a segment of the web material. In practice, RFID straps are manufactured in large continuous arrays in a roll-to-roll process that produces many thousands of straps.
In conventional RFID manufacturing systems, the RFID straps are diced from the web array, and assembled with antennas to form a complete RFID device, before any functional RF testing is performed. At this point in the manufacturing process, an assembled RFID device may fail functional testing if the antenna connection is poor or if the RFID chip is defective. If the cause of failure is a defective RFID chip that could have been identified before the final assembly step, then the time and cost associated with the antenna assembly process is wasted.